Abstract

We fabricate periodic arrays of simple-square and composite-square air hole nanostructures on a 120 nm thick Aufilm deposited on glass substrate by focused ion beam technology and study their optical properties by examining the optical near-field distribution via scanning near-field optical microscopy in the near-infrared region. The simple-square nanostructure only contains one square air hole in each unit cell, while the composite-square one contains the same size square air hole in the center and eight smaller square air holes in the periphery. The measured optical near-field patterns for the two nanostructures show very different distribution features. High intensity light spots locate within the central square air hole in the simple-square structure, while they sit at the peripheral smaller square air holes in the composite-square structure. Numerical simulations based on the plane-wave transfer-matrix method have been carried out to analyze the optical near-field patterns for the two metallic nanostructures and agree well with the experimental data. The results indicate that light interaction with metallic nanostructures is very sensitive to even a small change in the subtle geometrical feature. Meanwhile, by comparing near-field patterns with dielectricnanostructures theoretically, we also find that optical confinement is better for goldnanostructures than for dielectricnanostructures.

The authors would like to acknowledge the financial support from the National Natural Science Foundation of China under Contract Nos. 10525419 and 60736041 and the National Key Basic Research Special Foundation of China under Contract No. 2004CB719804.

Article outline:I. INTRODUCTIONII. SAMPLE PREPARATION AND EXPERIMENTAL SETUPIII. EXPERIMENTAL RESULTS FOR THE TWO METALLIC NANOSTRUCTURESIV. THEORETICAL RESULTS FOR THE TWO METALLIC NANOSTRUCTURESV. FURTHER DISCUSSIONSVI. CONCLUSION